Hi,
Skin on the breast is like skin anywhere else on the body.What you describe sounds more like a skin condition than a breast problem.You may want to have a dermatologist evaluate these brown spots and itchiness,since there is a variety of skin conditions that could be responsible.For example, it could be due to excessive sun exposure, genetics, hormones,skin fungus, seborrheic keratoses etc...and sometimes the cause is unknown.
It's impossible to tell you over the internet exactly what these brown spots may be....They have to be seen by a medical professional to obtain a correct diagnosis.
By the way, nipples could shrivel if its cold, or stimulated.If you haven't noticed any abnormal features like skin changes,inverted nipple,a breast lump, nipple discharge or have a sores that won't heal,then I don't think you should worry about it.
Take care...

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